Abstract
Atomic ions and free electrons embedded in condensed helium play important role in modern research on quantum fluids and solids. Here we present experimental and theoretical study of Ba+ cations immersed in superfluid He. We observe laser-induced fluorescence of Ba+ injected into liquid He from the plasma of radio frequency discharge in He-Ba gas mixture. The structure of trapping site is studied theoretically in the frame of the atomic bubble model making use of ab initio Ba+ - He pair potentials available in the literature. Calculated spectra of the ion are compared with the results of the experiment.
Highlights
Together with free electrons and He+ cations, Ba+ ion is a model object to study the properties of charged impurities in superfluid helium
The first mobility measurements of Ba+ in liquid He were reported back in 1972 by Johnson and Glaberson[1] and the first spectroscopic study was carried out by Reyher et al.[2] in 1986. It is well established since 1960-ies that free electrons in liquid He form cavity-like trapping sites, known as electron bubbles, whereas the positive He ions are surrounded by solid-like clusters of He, known as snowballs
II we develop the atomic bubble model (ABM) for Ba+ and it’s extension deformed bubble model (DBM)
Summary
Together with free electrons and He+ cations, Ba+ ion is a model object to study the properties of charged impurities in superfluid helium. The first mobility measurements of Ba+ in liquid He were reported back in 1972 by Johnson and Glaberson[1] and the first spectroscopic study was carried out by Reyher et al.[2] in 1986 It is well established since 1960-ies that free electrons in liquid He form cavity-like trapping sites, known as electron bubbles, whereas the positive He ions are surrounded by solid-like clusters of He, known as snowballs. The time of flight measurements[1,3,12,13] have shown that the alkali-earth cations, including Ba+, in superfluid He have slightly higher mobilities than the much lighter He+ ions in disagreement with the standard snowball model It was suggested by Cole and Bachman[4] that the trapping site may be better visualized as an atomic bubble with a radius of 4-5 Å surrounded by compressed, but not solidified, helium. IV we compare the observed and calculated spectra and discuss the applicability of the bubble model and its usefulness as a simplified model for this complex many-body system
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